Sheet-conveying apparatus and method for detection of multifeed thereof

ABSTRACT

A sheet-conveying apparatus and a method for detection of the multifeed thereof are provided. The sheet-conveying apparatus includes a passageway, a sheet-transporting mechanism and a sheet-detecting device. The sheet-detecting device disposed in the passageway includes a first transmitter, a first receiver, a second transmitter and a second receiver. A first signal is transmitted from the first transmitter along a first transmitting path and received by the first receiver. A second signal is transmitted from the second transmitter along a second transmitting path and received by the second receiver. The second transmitting path is oblique to the first transmitting path. The sheet-detecting device further includes a control-process unit for determining if the condition of the multifeed has occurred in the sheet-conveying apparatus according to the variations in the first signal and the second signal respectively received by the first receiver and the second receiver.

This application claims the benefit of Taiwan application Serial No. 96116187, filed May 7, 2007 the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a sheet-conveying apparatus, and more particularly to a sheet-conveying apparatus capable of detecting multiple sheets.

2. Description of the Related Art

Currently, printers, scanners, copiers, multi-functional machines or plotters are equipped with a sheet-conveying apparatus such as an automatic document feeder (ADF) and do not require the user to feed in sheets manually. The sheet-conveying apparatus feeds the sheets which are placed in a sheet supply tray, into the above electronic device one by one in a normal condition, but the automatic document feeder (ADF) can't completely avoid feeding sheets in a condition of the multifeed. When the multifeed occurs, the electronic device would fail to capture the images on the sheets. Besides, the condition of the multifeed may cause paper jam inside the electronic device and consequently cause the operation of the electronic device to suspend.

At present, the detection of the multifeed is achieved by providing a pin or a sensing arm in the passageway so that the presence of the sheets passing through the passageway and the change in the thickness of the sheets are detected. In such detecting method, if the thickness of the sheets detected is thicker than a predetermined thickness, then the condition of the multifeed is determined. However, such detecting method tends to be low in sensitivity, and sensing speed, while not able to reduce the chance of paper jam.

SUMMARY OF THE INVENTION

The invention is directed to a sheet-conveying apparatus and a method for detection of the multifeed thereof. Multiple sets of transmitters and receivers are used in the sheet-conveying apparatus, and at least one set of a transmitter and a receiver is obliquely disposed in the passageway of the sheet-conveying apparatus so as to enhance the detecting effect.

According to a first aspect of the present invention, a sheet-conveying apparatus for detection of the multifeed is provided. The sheet-conveying apparatus includes a passageway, a sheet-transporting mechanism and a sheet-detecting device. The passageway is for a sheet to be conveyed along a conveying path. The sheet-transporting mechanism conveys a sheet through the passageway. The sheet-detecting device includes a first transmitter, a first receiver, a second transmitter and a second receiver. The first transmitter transmits a first signal along the first transmitting path and the first receiver receives the first signal. The second transmitter transmits a second signal along the second transmitting path which is oblique to the first transmitting path, and the second receiver receives the second signal.

According to a second aspect of the present invention, a method for detection of the multifeed is provided. The method includes the following steps. Firstly, transmitting a first signal along a first transmitting path by a first transmitter, and transmitting a second signal along a second transmitting path by a second transmitter, wherein the second transmitting path is oblique to the first transmitting path. Next, receiving the first signal by a first receiver and receiving the second signal by a second receiver. Then, transmitting the first signal and the second signal from the first receiver and the second receiver to a control-process unit, and the control-process unit determines whether the multifeed occurs according to the variations in the first signal and the second signal.

The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sheet-conveying apparatus according to a preferred embodiment of the invention;

FIG. 2 is a flowchart of a first method for detection of the multifeed of the sheet-conveying apparatus of FIG. 1;

FIG. 3A-3B are perspective views of the sheet-conveying apparatus of FIG. 1 when the sheet-conveying apparatus is operated to detect the presence of the sheets; and

FIG. 4 is a flowchart of a second method for detecting multiple sheets of the sheet-conveying apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

A sheet-conveying apparatus and a method for detection of the multifeed thereof are provided in the present embodiment of the invention. The sheet-conveying apparatus detects whether the multifeed has occurred in the sheet-conveying apparatus by using the elements disposed therein.

Referring to FIG. 1, a perspective of a sheet-conveying apparatus according to a preferred embodiment of the invention is shown. As indicated in FIG. 1, the sheet-conveying apparatus 1 includes a sheet-transporting mechanism (not illustrated), a passageway and a sheet-detecting device. The passageway 10 is for a sheet to be conveyed along a conveying path. The sheet-transporting mechanism conveys the sheet through the passageway 10. The sheet-detecting device includes a first transmitter 12, a first receiver 14, a second transmitter 16, a second receiver 18 and a control-process unit 20. The first transmitter 12 and the first receiver 14 are disposed on the opposite sides of the passageway 10. The first transmitter 12 transmits a first signal along a first transmitting path P1 and the first receiver 14 receives the first signal. The second transmitter 16 and the second receiver 18 are disposed on the opposite sides of the passageway 10. The second transmitter 16 transmits a second signal along a second transmitting path P2 and the second receiver 18 receives the second signal. The second transmitting path P2 is oblique to the first transmitting path P1.

Preferably, the transmitting path between a transmitter and a receiver is perpendicular to the conveying path of the sheet. In the present embodiment of the invention, the first transmitting path P1 between the first transmitter 12 and the first receiver 14 is perpendicular to the conveying path of the sheets 100 and 200. The second transmitter 16 and the second receiver 18 are obliquely disposed in the passageway 10, so that the second transmitting path P2 and the first transmitting path P1 form a contained angle θ.

The first transmitter 12 and the second transmitter 16 are ultra-sound wave transmitters. The first receiver 14 and the second receiver 18 are ultra-sound wave receivers. The ultra-sound signals transmitted from the first transmitter 12 and the second transmitter 16, after passing through a sheet, are received respectively by the first receiver 14 and the second receiver 18. A decay in the energy of the ultra-sound signal relates to the density of the media that the ultra-sound wave passes through: higher the density of media is, larger is the decay in the energy of the ultra-sound signal. The control-process unit determines whether the multifeed has occurred by measuring the variations in the first signal and the second signal. Besides, the decay in the energy of the ultra-sound wave also relates to the thickness of the media that the ultra-sound wave passes through. The ultra-sound wave can be used to detect sheets types within a particular paper weight range as well. Moreover, a phase shift of the ultra-sound wave will occurs in the condition of the multifeed, such that the ultra-sound wave is able to detect whether there are multiple sheets in the passage way.

The sheet-transporting mechanism of the sheet-conveying apparatus 1 feeds the sheets into the passageway 10 one by one in a normal condition. As indicated in FIG. 1, when the sheet-transporting mechanism of the sheet-conveying apparatus in a abnormal condition that the sheet 100 and the sheet 200 are fed into the passageway 10 at the same time, the condition of the multifeed of the sheet-conveying apparatus 1 can be detected by the operation of the first transmitter 12, the first receiver 14, the second transmitter 16, the second receiver 18 and the control-process unit 20. Two detecting methods are disclosed in the present embodiment of the invention with accompanied drawings.

Referring to FIG. 2, a flowchart of a first method for detection of the multifeed of the sheet-conveying apparatus of FIG. 1 is shown. Also, referring to FIGS. 3A˜3B, perspective views of the sheet-conveying apparatus of FIG. 1 when the sheet-conveying apparatus is operated to detect the presence of the sheets are shown. As indicated in FIG. 2, the first method for detection of the multifeed of the sheet-conveying apparatus 1 includes steps 21˜23. Firstly, transmitting a first signal along a first transmitting path P1 by the first transmitter 12, and transmitting a second signal along a second transmitting path P2 by the second transmitter 16, wherein the second signal is transmitted along the second transmitting path P2 oblique to the first transmitting path P1. Next, receiving the first signal by the first receiver 14 and receiving the second signal by the second receiver 18, then the first signal and the second signal are transmitted to the control-process unit 20 from the first receiver 14 and the second receiver 18. Then, the control-process unit 20 determines if the condition of the multifeed occurs by measuring the variations in the first signal and the second signal.

In step 21, 22, when the sheet-conveying apparatus 1 feeds in a sheet, the control-process unit 20 controls the first transmitter 12 and the second transmitter 16 to transmit two ultra-sound signals (the first signal and the second signal), where the first transmitter 12 and the second transmitter 16 may transmit the ultra-sound signals at the same frequency or at different frequencies. In the present embodiment of the invention, the frequency of the first signal and the frequency of the second signal are the same. As indicated in FIG. 3A, when the feeding operation just begins, the first signal transmitted from the first transmitter 12 only passes through the sheet 100, but the second signal transmitted from the second transmitter 16 passes through both the sheet 100 and the sheet 200. The phase of the second signal shifts due to the interface between the sheet 100 and the sheet 200. Therefore, despite the frequency of the first signal is the same as the frequency of the second signal, the signal received by the first receiver and the signal received by the second receiver are different. Moreover, the second transmitter 16 and the second receiver 18 are obliquely disposed in the passageway 10, and the variations of signals become even more significant.

The signals received by the first receiver 14 and the second receiver 18 are converted into a third signal and a fourth signal, and transmitted to the control-process unit 20. As indicated in step 23, the control-process unit 20 determines the phase shift ψ1 between the first signal and the third signal, and the phase shift ψ2 between the second signal and the fourth signal. The control-process unit 20 then compares the phase shift ψ1 and the phase shift ψ2 to determine whether the condition of the multifeed has occurred in the sheet-conveying apparatus 1 according to the difference between the phase shift ψ1 and the phase shift ψ2.

When the first signal is transmitted from the first transmitter 12 and the second signal is transmitted from the second transmitter 16 to pass through the sheets 100 and 200, the decay in the energy of the ultra-sound signals will occur due to a space in between the sheet 100 and the sheet 200. As indicated in FIG. 3B, there is a distance D1 between the sheet 100 and the sheet 200. As the first transmitting path P1 is perpendicular to the conveying path of the sheet, the decay in the energy of the first signal transmitted from the first transmitter 12 relates to the distance D1, and the decay of the second signal transmitted from the second transmitter 16 relates to the distance D2 (D2=D1/cos θ). Thus, the decay 61 has occurred between the first signal which is transmitted from the first transmitter 12 and the third signal which is received by the controlling-process unit 20, and the decay 62 has occurred between the second signal which is transmitted from the second transmitter 16 and the fourth signal which is received by the controlling-process unit 20. The sheets make an absorption-like effect generates by transmitting the ultra-sound signals through the sheets and the decay in the energy of the ultra-sound signals has occurred. As the second transmitter 16 and the second receiver 18 are obliquely disposed in the passageway 10, the decay 61 differs from the decay δ2.

According to the above method, the ultra-sound signals of the same frequency are transmitted for detection of the multifeed. In other embodiment, the ultra-sound signals of different frequencies can also be transmitted for detection of the multifeed. The ultra-sound wave of a higher frequency is more sensitive to the thickness of the sheet than the ultra-sound wave of a lower frequency is, so the sensitivity of detection can be increased by increasing the frequency of the ultra-sound signal.

Referring to FIG. 4, a flowchart of a second method for detection of the multifeed of the sheet-conveying apparatus of FIG. 1 is shown. As indicated in FIG. 4, the second method for detection of the multifeed of the sheet-conveying apparatus 1 includes steps 41˜43. Firstly, at a first time, transmitting a first signal from the first transmitter 12 along the first transmitting path P1, and receiving the first signal by the first receiver 14, then transmitting the first signal to the control-process unit 20. Next, at a second time, transmitting a second signal from the second transmitter 16 along a second transmitting path P2 oblique to the first transmitting path P1, and receiving the second signal by the second receiver 18, then transmitting the second signal to the control-process unit 20. Lastly, the control-process unit 20 determines whether the multifeed has occurred according to the variations in the first signal and the second signal.

The difference between steps 21˜23 of the first method and steps 41˜43 of the second method is that the ultra-sound signals in the second method are transmitted from the first transmitter 12 and the second transmitter 16 at different times. However, the method of measuring variations (such as phase shift and energy decay) in the second method is the same as the method of measuring variations in the first method, thereby effectively detecting the condition of the multifeed in the sheet-conveying apparatus 1.

The present embodiment of the invention is exemplified by two sets of the transmitters and the receivers. However, in other embodiment, more than two sets of the transmitters and the receivers can be used for detection of the multifeed, provided that at least one set of the transmitter and the receiver is obliquely disposed. For paper whose basis weight ranges from 50 g/m² to 120 g/m², the frequencies of the signals transmitted by the first transmitter 12 and the second transmitter 16 had better be set at higher than 40 kHz, particularly between 200 kHz and 300 kHz, in order to get an accurate result.

The sheet-conveying apparatus 1 is commonly used in the electronic devices such as the scanner, copier and multi-functional machine for feeding documents or blank sheets into the electronic device one by one. When multiple sheets are fed into the electronic device by the sheet-conveying apparatus 1, the condition of the multifeed may cause paper jam inside the electronic device and consequently cause the operation of the electronic device to suspend. The sheet-conveying apparatus 1 installed in the electronic device can effectively solve the problem stated above. The subsequent processing steps of the electronic device in the event that the electronic device detects the condition of the multifeed are elaborated below.

1. The electronic device will stop current operation or directly convey the overlapping sheets to the discharge tray. And the electronic device displays on its control panel or screen a message alerting users that the multifeed has occurred.

2. The electronic device continues to operate but only finishes scanning the sheet that has reached the image capturing area when the multifeed is detected. After the scanning is completed, the warning message will be displayed on the control panel or the screen.

A sheet-conveying apparatus and a method for detection of the multifeed thereof are disclosed in the above embodiment of the invention. More than two sets of ultra-sound wave transmitters and receivers may be used in the sheet-conveying apparatus, and at least one set of transmitter and receiver is obliquely disposed with respect to the surface of the sheet being conveyed. The detection of the multiple sheets becomes more effective as the ultra-sound wave transmitter and receiver are obliquely disposed. Besides, the ultra-sound wave transmitters may transmit signals of the same or different frequencies at the same time or at different times, and therefore the present invention provides a number of approaches to detect the multifeed.

While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures. 

1. A sheet-conveying apparatus, comprising: a passageway for a sheet to be conveyed along a conveying path; a sheet-transporting mechanism for conveying the sheet through the passageway; and a sheet-detecting device disposed in the passageway, having: a first transmitter for transmitting a first signal along a first transmitting path; a first receiver for receiving the first signal; a second transmitter for transmitting a second signal along a second transmitting path; and a second receiver for receiving the second signal; wherein the second transmitting path is oblique to the first transmitting path.
 2. The sheet-conveying apparatus according to claim 1, wherein the first transmitting path is perpendicular to the conveying path.
 3. The sheet-conveying apparatus according to claim 1, wherein the first transmitter transmits the first signal and the second transmitter transmits the second signal at the same time or at different times.
 4. The sheet-conveying apparatus according to claim 1, wherein the first transmitter transmits the first signal at a first frequency same as a second frequency at which the second transmitter transmits the second signal.
 5. The sheet-conveying apparatus according to claim 1, wherein the first transmitter transmits the first signal at a first frequency different from a second frequency at which the second transmitter transmits the second signal.
 6. The sheet-conveying apparatus according to claim 1, wherein when the weight of the sheet ranges from 50 g/m² to 120 g/m², at least one of the first transmitter and the second transmitter transmits a signal whose frequency is higher than 40 kHz.
 7. The sheet-conveying apparatus according to claim 6, wherein at least one of the first transmitter and the second transmitter transmits a signal whose frequency ranges from 200 kHz to 300 kHz.
 8. The sheet-conveying apparatus according to claim 1, wherein the first transmitter and the second transmitter are ultra-sound wave transmitters, and the first receiver and the second receiver are ultra-sound wave receivers.
 9. The sheet-conveying apparatus according to claim 1, wherein the sheet-detecting device further comprises a control-process unit electrically connected to the first receiver and the second receiver for determining if multiple sheets are conveyed in the passageway according to the variations in the first signal and the second signal respectively received by the first receiver and the second receiver.
 10. The sheet-conveying apparatus according to claim 1, wherein the first transmitter and the first receiver are respectively disposed on opposite sides of the passageway.
 11. The sheet-conveying apparatus according to claim 1, wherein the second transmitter and the second receiver are respectively disposed on opposite sides of the passageway.
 12. A method for detecting multiple sheets, comprising: transmitting a first signal along a first transmitting path by a first transmitter; transmitting a second signal along a second transmitting path oblique to the first transmitting path by a second transmitter; receiving the first signal by a first receiver; receiving the second signal by a second receiver; and determining if multiple sheets are conveyed along a conveying path according to the variations in the first signal and the second signal.
 13. The method according to claim 12, wherein the step of determining if multiple sheets are conveyed along a conveying path according to the variations in the first signal and the second signal comprises: detecting the decay in the amplitude of the first signal and the second signal.
 14. The method according to claim 12, wherein the step of determining if multiple sheets are conveyed along a conveying path according to the variations in the first signal and the second signal comprises: detecting the phase shift of the first signal and the second signal respectively.
 15. The method according to claim 12, wherein the first transmitter transmits the first signal and the second transmitter transmits the second signal at the same time.
 16. The method according to claim 12, wherein the first transmitter transmits the first signal and the second transmitter transmits the second signal at different times.
 17. The method according to claim 12, wherein the first transmitter transmits the first signal at a first frequency same as a second frequency at which the second transmitter transmits the second signal.
 18. The method according to claim 12, wherein the first transmitter transmits the first signal at a first frequency different from a second frequency at which the second transmitter transmits the second signal.
 19. The method according to claim 12, wherein when the weight of the sheet ranges from 50 g/m² to 120 g/m², at least one of the first transmitter and the second transmitter transmits a signal whose frequency is higher than 40 kHz.
 20. The method according to claim 19, wherein at least one of the first transmitter and the second transmitter transmits a signal whose frequency ranges from 200 kHz to 300 kHz. 